919
FXUS66 KPDT 222304
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
304 PM PST Sat Feb 22 2025

.SHORT TERM...Today through Monday...

Bottom Line Up Front

1) Moderate mountain rain/snow, light lowland rain to start

2) Breezy to windy conditions through Sunday night

3) Hydrological concerns Monday

Current satellite shows high clouds across the area as the upper
level trough begins to push onshore. Current radar is showing the
warm front has begun to move across the area bringing light rainfall
to the WA Cascade crests. Temperatures along the foothills of the
northern Blues have risen above 60s with the downsloping off of the
Blues.

Sunday through Monday night, models show a wet upper level coupled
with a strong atmospheric river making its way across the region
exiting by Monday night. Both the GFS and ECMWF IVT ensemble suites
show close to a 100% chance of IVT values greater than 250 kg/m/s
making it east of the Cascade crest. This will allow for relatively
moderate rainfall accumulations along the mountains, with locally
moderate rainfall across the lower elevations. The NBM 48-hr
probabilities ending Monday morning for precipitation accumulations
shows 95-100% probabilities along the Cascade crest and east slopes
with 70-90% probabilities along the northern Blues for 1 inch of
rain. At 2 inches or higher, probabilities are 70-90% along the
Cascade crest, 35-55% probabilities along the higher terrain of the
northern Blues. Snow levels will be relatively high to begin with
Sunday through Monday afternoon before dropping steadily decreasing
with the models showing the snow levels nearing 4500 feet. Models
show there is snow expected to fall above 4500 feet Monday night
with the highest amounts along the higher crests. 60-80% of the raw
ensembles show there to be between 0.01-0.04 inches along the crests
of the eastern mountains and northern Blues.

Breezy conditions will accompany the system this afternoon ahead of
the shortwave trough and warm front. Model guidance shows surface
pressure gradients across the Northern Blue Mountains of OR will
increase to around 10-12mb this evening and overnight bringing the
strongest winds (gusts between 40-50mph) through the Grande Ronde
valley and along the Blue Mountain foothills of OR and WA as well as
later into central OR through Sunday afternoon and lingering through
Sunday night with high confidence of 70-90%. Wind advisories will
begin for all areas mentioned at 4 PM and remain in affect through
10 PM Sunday. As for central OR, the wind advisory will begin at 4
PM Sunday and continue until 10 PM.

Lastly and most importantly, there are some hydrological concerns
that are popping up from all the warm temperatures and
precipitation. Rivers through the Yakima, Naches, Klickitat, Walla
Walla and the lower Yakima River Basins will see rises in the rivers
within the Naches at Cliffdell forecasted to break above bankfull by
Monday with probabilities of 10-25%, Walla Walla River near Touchet
with probabilities of 25-75% breaching action stage and Klickitat
River near Pitt 10-25% reaching action stage as well. A hydrologic
outlook has been issued and we will continue to closely monitor the
river forecasts and work with the river centers as the day draws
closer. In the meantime, be prepared and continue to remain vigilant
and check the website for updated information regarding the rivers.
Bennese/90

.LONG TERM...Tuesday through Saturday...Ensemble consensus points
toward that of a more benign, spring-like pattern for next week,
with only limited chances for precip through the work week and temps
in the lower elevations wavering around the upper 50s and low 60s.
These generally quiet conditions will lead to chilly overnights with
lows in the 30s, but temps overall will run 5-10 degrees above
average - a nice break from what has otherwise been a cold and snowy
February.

The last of the oncoming atmospheric river is expected to move out
by early Tuesday morning. Light, lingering mountain precip may last
through the morning (PoPs generally 30-50%), before dry conditions
prevail in the afternoon as ridging starts to build in. Ensemble
clustering shows little break in this ridging through the work week,
with deterministic guidance showing potentially a weak upper-level
wave to our north briefly flattening the ridge, but still leaving us
under benign zonal flow. Nothing to note synoptically until the
weekend, when guidance tries to bring in a trough late Saturday into
Sunday. GFS and ECMWF show a good amount of unity between each other
on the upper-level pattern through the week, while clusters show
solutions falling out of sync by the start of next weekend. Majority
of guidance does depict a system arriving next weekend, but until
then, PoPs will be limited to the high mountains, with little if any
precip expected to occur. Overall forecast confidence falls around
60-70%, with only complicating factor being the potential impacts of
next weekend`s system. Evans/74


&&

.AVIATION...00z TAFs...An atmospheric river moving into the region
this evening will provide sites with a round of intermittent rain
lasting through much of the weekend, as well as gusty winds at most
sites. Rain is expected to encompass all sites by 03z at the latest,
with a brief break expected overnight, before resuming around
daybreak Sunday. Winds have started to pick up across most sites,
and are expected to peak overnight into Sunday, with sites
potentially seeing gusts over 30 kts. DLS and PSC will largely be
spared of the strongest winds. Conditions may dip into MVFR at times
under rainfall, but winds are expected to keep cigs elevated enough
(3-6 kft under rain) to preclude the possibility of IFR or worse
conditions. LLWS has also been mentioned for various sites as winds
start to pick up this evening. Evans/74


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  47  65  41  61 /  60  90  70  70
ALW  45  62  41  57 /  80 100  90  70
PSC  44  66  38  57 /  80  70  50  60
YKM  40  61  33  49 /  60  80  50  80
HRI  45  60  39  61 /  60  70  50  70
ELN  38  54  33  46 /  80  80  60  80
RDM  43  63  37  59 /  60  70  50  60
LGD  37  50  35  48 /  90 100  90  70
GCD  40  55  37  53 /  90  90  60  70
DLS  46  61  41  55 /  80  90  70  90

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...Wind Advisory until 10 PM PST Sunday for ORZ049-507-508.

     Wind Advisory from 4 PM to 10 PM PST Sunday for ORZ511.

WA...None.
&&

$$

SHORT TERM...90
LONG TERM....74
AVIATION...74